A lumen in a human or animal body, such as a blood vessel or a urinary tract, can require internal support to ensure proper flow of fluid in the lumen. For example, a lumen can become at least partially occluded, and support can be required to reestablish sufficient internal bore in the lumen for flow of fluid.
Support for a lumen can be provided by implantation of a stent in the lumen. In many situations, this can allow a patient to resume normal activities without dependence on medical help, at least temporarily and in many situations indefinitely.
It can also be desirable to provide support in a lumen temporarily, without necessarily implanting a stent in the lumen. This can be achieved by means of a catheter which can be inserted into a lumen, and which has a portion which can be inflated by means of fluid supplied to the inflatable portion through a hollow bore of the catheter. This technique is referred to as "balloon angioplasty" when applied to blood vessels.
In processes in which inflatable catheters are used, the occlusion and the walls of the lumen are expanded and stretched by inflation of the catheter. The walls then remain in the stretched condition so as to remove or at least to reduce the occlusion, and to establish an increased flow of fluid in the lumen.
Once inflated, the catheter completely blocks the lumen against flow of liquid. The expansion process must therefore be carried out quickly, and then the catheter must be deflated quickly to reestablish flow of fluid. This is particularly critical in blood vessels on or near the heart which, if deprived of blood flow for even short periods (sometimes less than 30 seconds) can give rise to the condition known as "heart attack".
The present invention provides an expander assembly which includes a shape memory alloy component, which exhibits a shape memory effect. Shape memory alloys are discussed in an article by L. McDonald Schetky in the Encyclopedia of Chemical Technology (edited by Kirk-Othmer), volume 20, pages 726 to 736. Subject matter disclosed in that document is incorporated in this specification by this reference to the document. Such alloys can exist in martensite and austenite phases. An article formed from the alloy while in the austenite phase can be deformed, after it has been cooled so that the alloy is in the martensite phase. If the temperature of the article is subsequently increased so that the alloy transforms back to the austenite phase, the article reverts to the configuration which it had before it was deformed. The transformation from austenite phase to martensite phase takes place over the temperature range M.sub.s to M.sub.r, and the transformation from martensite phase to austenite phase takes place over the temperature range A.sub.s to A.sub.f.